This document describes and presents initial results for the health-impact assessment related to adding more native plants to City of Denver. We aim to estimate the number of deaths that would be prevented by adding more green space, specifically native plants, to the City of Denver. We estimate the number of deaths prevented corresponding to three broad greening scenarios, which were informed by conversations with local stakeholders. The scenarios are:
For all scenarios, we measured green-space exposure by the normalized difference vegetation index (NDVI) measured by the Landsat-8 satellite at a spatial resolution of 30 meters squared. To determine the target NDVI value, we measured the NDVI of a 100% native zone in the Denver Botanic Gardens on several cloud-free spring and summer days. The NDVI value was about 0.5 in this area, so we assumed that, by adding more native plants to places in Denver, the NDVI of those areas would change to 0.5.
We first measured the mean NDVI of each census block group on July 4, 2021. The weighted block-group-level mean is presented here, weighted by the proportion each 30 square-meter pixel covers by the census block group. For example, if half of a pixel overlaps the block group, it receives a weight of 0.5 in the weighted average. We also removed bodies of water before measuring NDVI.
We excluded census block whose baseline NDVI was above the native-plant threshold:
We measured NDVI in a 200-foot buffer, a 100-foot buffer, and a 50-foot buffer around all bodies of water in Denver. We downloaded bodies of water from OpenStreetMap (code here. We defined residential exposure to these riparian areas as those individuals living within a 500-meter buffer, following the green-space literature that has defined green-space exposure based on residential proximity. We estimated the number of people in this buffer by multiplying the population density of the census block group by the intersecting area.
The below map depicts mean NDVI in the portions of census block groups that intersect a 200-foot buffer as well as those pieces that intersect the part of the 500 m buffer that would not be intervened upon, i.e., the part between the 200-foot buffer and the edge of the 500 m buffer.